Air conditioner with a liquid to suction heat exchanger

ABSTRACT

An air-conditioner having a compressor, a condenser and an evaporator. The air-conditioner further includes a liquid-to-suction heat exchanger provided in a flowpath from the condenser to the evaporator.

TECHNICAL FIELD

The present disclosure relates to an air-conditioner. In particular the present disclosure relates to a portable air-conditioner.

BACKGROUND

Air conditioning (AC) is a collective expression for conditioning air into a desired state. It could be heating the air during cold periods, cooling the air during warmer periods or for cleaning the air if it contains unwanted particles. However, the expression air conditioning is most often used when emphasizing cooling. As a product, air conditioners can look and be used in various ways, but they all share the same basic technology.

Existing portable air-conditioners are often found to be large, hard to handle, noisy and inefficient. Furthermore, the connected exhaust air outlet that removes the heat from the room is often complicated and inefficient in its design. A known portable air-conditioner is for example described in the U.S. Pat. No. 2,234,753.

The design of portable AC systems differs from other Air Conditioners because all the components of the system are mounted inside of a packed unit which has to work inside of the conditioned space, releasing the residual energy (generated in the normal cooling process) through an air exhaust system which is usually connected to the outside.

In portable AC units there are two general procedures to cool down an air source condenser: single duct and dual duct methods. In the first one (single duct), the system takes air from its surroundings (conditioned space), forcing it to pass through the condenser surface and eventually removing the residual energy from it. Then, the hot air is expelled outdoors by using a single duct system. In this method, the intake air temperature has the indoor temperature conditions, which makes the energy exchange process more beneficial from standpoint of the refrigerant cycle.

In the dual duct method, the system uses an air intake duct to inject “hot” air from outdoor to cool down the condenser. Eventually the air coming from condenser at a relatively high temperature is released outdoors again by a secondary exhaust duct. In this method the air intake temperature is at the outdoor temperature conditions. This method can provide a quicker cooling effect for the user, since the system is not using the indoor air as a coolant media for condenser, but requiring in turn a larger size/volume of components to compensate the higher inlet outdoor temperatures.

Both methods, single and dual duct, have different limitations in terms of: air flow rates, size of the heat exchangers and also dimensions of the air piping system.

Those particularities requires that the portable AC systems make use of particular size of condensers, limiting the maximum air flow rate used by the system, since the air intake and air exhaust systems have to be as much compact as possible.

Air flow rates in portable AC systems are also limited by the noise levels, since larger air flow rates flowing through small diameter hoses lead to higher pressure drops and higher noise levels. In that sense, the single duct systems have a clear advantage over the dual duct systems, because the temperature difference between the intake air and the condensing temperature of the cycle is larger, requiring lower air flow rates to perform the heat rejection process.

So, for portable AC systems, the condenser is one of the most critical components to design, since it has to exchange higher heat loads with a very limited air flow rate. Therefore, that particularity affects in a significant way the whole design of the condenser and the whole system performance.

There is a constant desire to improve the operation of air-conditioners.

Hence, there is a need for an improved air-conditioner.

SUMMARY

It is an object of the present invention to provide an improved air-conditioner that at least partly solves problems with existing air-conditioners.

This object and others are obtained by the air conditioner as set out in the appended claims. Also disclosed are devices that can be used together with air-conditioner, in particular portable air-conditioners.

In accordance with one embodiment an air-conditioner comprising a compressor, a condenser, and an evaporator is provided. The air-conditioner comprises a liquid-to-suction heat exchanger provided in the flowpath from the condenser to the evaporator. Hereby an improved efficiency of the air conditioner can be achieved. The air-conditioner can advantageously be a portable air-conditioner.

In accordance with some embodiments the air-conditioner can comprise a four-way valve for reversing the refrigeration cycle to allow the air-conditioner to provide both heating and cooling.

In accordance with some embodiments a liquid line to the liquid-to suction heat exchanger of the air-conditioner is arranged inside of a saturated vapour line that comes from evaporator. The liquid line can be provided with fins on the outside of the liquid line.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail by way of non-limiting examples and with reference to the accompanying drawings, in which:

FIGS. 1 and 2 illustrate different cooling effects,

FIG. 3 illustrates the influence of the internal superheat on the energy efficiency ratio,

FIG. 4 illustrates the negative effect of the external vapour superheat over the system performance,

FIG. 5 shows the volumetric cooling effect and EER increase for different refrigerants as a function of the subcooling increase after the saturation conditions,

FIG. 6 shows the volumetric cooling effect and EER increase for different refrigerants as a function of the internal superheat increase, after the saturation conditions,

FIG. 7 depicts an exemplary air-conditioning system,

FIG. 8 depicts an exemplary air-conditioning system in accordance with an alternative embodiment,

FIG. 9 depicts different configurations for the liquid-to-suction heat exchanger,

FIG. 10 illustrates a liquid line located around or in parallel to the vapour suction line, and

FIG. 11 illustrates the general principles of an air conditioner system.

DETAILED DESCRIPTION

FIG. 11 illustrates the general principles of an air conditioner system. The main parts of the system are the compressor 1101, evaporator 1103, condenser 1105, and expansion device 1107 such as a capillary tube. Also a condenser fan 1109 and an evaporator fan 1111 can be provided. The compressor is connected in a circuit with the condenser, the evaporator, and the expansion device. The refrigerant has the ability to turn from liquid into vapor, and by that change in temperature. The tempered refrigerant and the indoor air work in symbiosis to exchange heat to each other.

To increase the performance of an air-conditioner, in particular a portable air-conditioner liquid-to-suction heat exchangers are provided as a complementary element for the basic refrigeration cycles in order to increase their cooling capacity and cycle efficiency.

The technology of liquid-to-suction heat exchangers allows the energy exchange process between the liquid refrigerant after condenser and the saturated vapour that returns to the compressor suction.

Hence liquid-to-suction heat exchangers are provided in Air-conditioner systems in particular in portable air-conditioners.

Some different implementations of liquid-to-suction heat exchanger in air-conditioners are described. In a general, a liquid to suction heat exchanger comprises in one of its circuits, a single or multiple liquid line that encloses the liquid refrigerant coming from condenser of the air-conditioner. In its second circuit the heat exchanger encloses the saturated or slightly superheated refrigerant that leaves the evaporator of the air-conditioner.

The energy exchange between both flows allows the increase of the subcooling degree of the liquid refrigerant, just before it enters into the expansion device, while the vapour coming from evaporator gains an extra degree of superheat, just before it enters to the compressor suction to restarts the cooling cycle again.

An additional subcooling degree after condenser typically provides a positive effect in the total cooling capacity of the refrigeration cycles, since a higher subcooling degree will allow higher evaporation enthalpies and subsequently higher cooling capacities in the evaporator.

FIG. 1 shows the effect on the volumetric cooling capacity and Energy efficiency ratio (EER) as a function of the subcooling degree for the refrigerant R410A, commonly used in portable air conditioners. FIG. 1 represents the thermodynamic effect of the liquid-to-suction heat exchanger as a function of different condensing and evaporating temperatures, commonly achieved in AC applications.

In FIG. 1. the volumetric cooling effect and EER (Energy Efficiency ratio) increase as a function of subcooling degree, at 10° C. of evaporating temperature (left), and 50° C. of condensing temperature (right), using R410A as cooling media is depicted.

From FIG. 1 it is clear that the subcooling degree has always a positive effect in the cycle performance, especially at high condensing temperatures. This fact is especially advantageous in portable Air-conditioning (AC) units which have limited air flow rates in the condenser side, due to the space restrictions intrinsically related to this kind of systems, and where the condensing temperatures tend to be high.

The increase of the subcooling degree after the condensation is especially beneficial for air-cooled condensers. However, the increase of the subcooling inside of condenser leads the increase of the internal volume and heat transfer areas, which is not always optimum from the economic standpoint.

In that sense, with the use of an external liquid subcooler the system can take advantage of the cold suction vapour temperature improving the cycle performance in an efficient way.

In a standard refrigeration cycle, the suction vapour line usually exchanges energy with the surroundings, wasting the refrigerant effect produced in the cycle by the low evaporation conditions.

The technology of liquid-to-suction heat exchangers offers the advantage of allowing the release of part of the heat load from the condensed liquid into the cycle through the suction gas line, increasing not only the subcooling degree of the liquid refrigerant but also increasing the temperature of the vaporised refrigerant before it enters into the compressor.

Additionally, the moderated increase of the suction temperature has the advantage to minimise the effect of heat gains from the environment, which is an extremely negative effect from the cycle standpoint. An additional superheating prevents also undesired condensation in the suction line, avoiding the need of additional insulation material over the pipes.

Although both effects seem beneficial for the cycle performance, the excessive increase of the superheat after the evaporator could for some specific refrigerants and certain circumstances represent a negative impact on the cycle performance since the volumetric refrigeration effect and volumetric compression work will depend on the specific volume of the suction gas.

FIG. 2 represents the effect on the volumetric cooling effect as a function of the internal suction vapour superheat (superheat created inside of the refrigerated space) for R410A, commonly used in AC units.

In FIG. 2, the volumetric cooling effect is represented at different condensing temperatures, fixing the evaporating temperature at 10° C. (FIG. 2-left); and different evaporating temperatures fixing the condensing conditions at 50° C. (FIG. 2-right).

From FIG. 2 it is clear that for R410A the internal superheat improves the volumetric cooling effect when cycle is working at condensing temperatures above 45° C. On the other hand, at high evaporating temperatures, the internal superheat has a negative effect on the volumetric capacity.

FIG. 3 shows the influence of the internal superheat on the energy efficiency ratio of an R410A system. From FIG. 3, it is clear that for condensing temperatures below 50° C. the internal superheat has a negative impact on the system performance. On the other hand, high evaporating temperatures have also a negative effect over the cycle performance.

FIG. 3. shows the EER of R410A in a standard cycle as a function of the internal superheat; at different condensing temperatures, fixing evaporation at 10° C. (left); and at different evaporating temperatures fixing the condensation at 50° C. (right).

For an AC application, standard condensing temperatures normally fluctuate between 48° C. to 60° C. while the evaporating temperatures vary around 8° C. to 12° C. That makes this technology suitable to improve the capacity and efficiency of AC cycles for portable applications using R410A.

Additionally, the use of the technology of liquid-to-suction heat exchangers proposed in the present invention represents a positive solution to minimise the detrimental influence of the heat transfer to the suction pipes from the surroundings. Another additional advantage is the minimisation of condensing moisture on the suction pipes surface.

FIG. 4 illustrates the negative effect of the external vapour superheat over the system performance. The external superheat is produced by the energy exchange between the suction line and its surroundings, outside of the refrigerant space. Its effect is always negative and has to be avoided as much as possible in any design, either by the use of a liquid to suction heat exchanger, by thermal insulation, or by an increase of the evaporating temperatures if the system conditions allow it.

FIG. 4 depicts decrease of EER for R410A in a standard cycle as a function of the external superheat; at different condensing temperatures, fixing evaporation at 10° C. (left); and at different evaporating temperatures fixing the condensation at 50° C. (right).

From the previous analysis it is clear that for certain conditions the implementation of a liquid to suction heat exchanger in a basic cycle can improve the cycle performance by the use of the standard refrigerant R410A, commonly used in AC applications in general and in particular in portable AC systems.

Further a comparison and analysis of some alternative refrigerants, as possible substitutes to the standard ones to be implemented in AC systems. The methodology used to compare the cycles is the same used in previous analysis for R410A.

FIG. 5 shows the volumetric cooling effect and EER increase for different refrigerants as a function of the subcooling increase after the saturation conditions. The comparison has been done at 50° C. of condensing temperature and 10° C. of evaporating temperature.

FIG. 5. Volumetric cooling effect and EER increase as a function of subcooling degree, at 10° C. of evaporating temperature and 50° C. of condensing temperature, for R410A, R32, R290, R1234YF, and R152a.

From FIG. 5, it is clear that the increase of the subcooling degree is always positive for the system performance. However, the benefit obtained by the increase of the system performance is higher for some refrigerants, like R1234YF, R410A or Propane. General trends shown before, regarding the effect of evaporation and condensation temperatures, are maintained for the refrigerants compared.

FIG. 6 shows the volumetric cooling effect (left) and EER increase (right) for different refrigerants as a function of the internal superheat increase, after the saturation conditions. The comparison has been done at 50° C. of condensing temperature and 10° C. of evaporating temperature. In FIG. 6 the volumetric cooling effect and EER increase as a function of internal superheat degree, at 10° C. of evaporating temperature and 50° C. of condensing temperature, for R410A, R32, R290, R1234YF, and R152a.

FIG. 6 show that unlike the subcooling, the increase of the internal superheat has a negative effect for some refrigerants considered as alternatives for AC systems. R32 has always a negative behaviour for the system performance, while R1234YF and R290 show the better effect in both, the volumetric cooling effect and EER.

As was shown previously, R410A shows a moderated improvement at 50° C./10° C., while the internal superheat of R152a shows a null effect over the system performance. This basically means that the increase of the subcooling by the use of a liquid-to-suction heat exchanger does not have a negative effect over the system performance, and only the subcooling degree will provide an increase of the system performance.

An exemplary configuration of an air-conditioning system is shown in FIG. 7. The air-conditioning system of FIG. 7 can for example be implemented in a portable air-conditioner. In the preferred embodiment the compressor discharge line is connected to the condenser inlet port. The condenser outlet is then connected to the liquid line that enters to the bottom side of the liquid-to-suction heat exchanger. From the liquid-to-suction heat exchanger, the refrigerant enters into the expansion device and then to the evaporator, which is connected in turn to the vapour circuit of the liquid-to-suction heat exchanger. Finally, the suction gas line of compressor is connected to the other end of the liquid-to-suction heat exchanger in its bottom side.

In FIG. 7, 701 represents a compressor, 702 is a discharge line, 703 is a condenser, 704 is a liquid line, 705 is an expansion device, 706 is a evaporator inlet line, 707 is an evaporator, 708 is a evaporator outlet line, 709 is a liquid-to-suction heat exchanger, 710 is a compressor suction line.

Hence, FIG. 7 depicts an AC unit using a liquid-to-suction heat exchanger 709. In the embodiment in FIG. 7 the liquid-to-suction heat exchanger 709 is provided in the flowpath from the condenser 703 to the evaporator 707.

In accordance with one embodiment a four-way valve for reversing the cycle and allowing the system to provide both heating and cooling is provided. In such an embodiment the compressor is connected to the for-way valve in its high pressure inlet port. The condenser and the evaporator are connected to the valve through its commute ports. The gas return port of the valve is connected to the liquid-to-suction heat exchanger in its upper side. Finally, the suction gas line of compressor is connected to the other end of the liquid-to-suction heat exchanger, in its bottom side.

The expansion device and the liquid line are placed in the similar manner as in the embodiment of FIG. 7, and it can be used a set of capillary tubes instead of an expansion valve. A possible implementation is depicted in FIG. 8. In FIG. 8, 801 represents a compressor, 802 is a discharge line, 803 is a 4 way valve, 804 is a condenser inlet line, 805 is a condenser, 806 is a liquid line, 807 is an expansion device, 808 is a evaporator inlet line, 809 is a evaporator, 810 is an evaporator outlet line, 811 is a gas return line from the 4 way valve, 812 is the liquid-to-suction heat exchanger, 813 is the compressor suction line.

Hence, FIG. 8. depicts an alternative embodiment for an AC unit using a liquid-to-suction heat exchanger that includes the use of a 4 way valve adapted to reverse the refrigeration cycle and provide heating.

Other embodiments include different geometries of the pipes and components that are used in the liquid to suction heat exchanger. FIG. 9 depicts different alternatives for the liquid-to-suction heat exchanger, in which the liquid line 704 is inside of the saturated vapour line that comes from evaporator.

In FIG. 9, 901 represents a saturated vapour line, 902 is a liquid line pipe, 903 represents vertical fins attached to the liquid line, 904 represents a helicoidally shaped fin attached to the liquid line.

Hence, FIG. 9 depicts different configurations for the liquid-to-suction heat exchanger. The different configurations all have the liquid line inside of the suction line. The different embodiments include smooth pipes and finned pipes.

In accordance with some embodiments for the liquid-to-suction heat exchanger as described herein the liquid line is located around or in parallel to the vapour suction line. FIG. 10 shows some possible options. In FIG. 10, 1001 represents a vapour suction line, 1002 is a set of one or more capillary tubes wrapped and welded around the suction line, in which is transported the liquid refrigerant, 1003 is a liquid line attached/welded in parallel to the suction line, 1004 represents a coaxial liquid line around the suction line.

In accordance with some embodiments capillary tubes are provided instead of an expansion valve.

Using the air-conditioner as described herein can increase the cooling capacity and efficiency of standard refrigeration cycles, and is particularly applicable to portable air conditioners.

The use of liquid-to-suction heat exchangers in an air-conditioner, in particular a portable air-conditioner offers the possibility to have a compact and efficient system, since this technology allows the use of part of the cooling capacity to generate an additional degree of subcooling in the refrigeration cycle.

This technology is particularly advantageous for AC systems with heavy restriction in the size of condenser and components and limitations in air flow rates.

The use of the technology of liquid-to-suction heat exchangers offers also the possibility to minimise the negative effects of the external superheat, which is always in detriment of the cycle performance.

Additionally, the use of liquid-to-suction heat exchangers prevents the condensation of moisture around the suction line in the system.

In a standard refrigeration cycles, the cooling capacity generated by the system is produced by the refrigerant mass flow rate pumped out by the compressor and the evaporation enthalpy of the refrigerant get from the evaporator.

Most of the systems require a proper dimensioning of condenser to reach the proper conditions of the refrigerant before it enters into the expansion device. However, for some specific systems the size of the condenser is limited for the space available in the system, leading to poor designs.

To increase the cooling capacity of the system, without increase the size of the compressor is by increasing the evaporation enthalpy reached in the evaporator. This is achieved by the use of a liquid-to-suction heat exchanger. 

1. An air-conditioner comprising: a compressor; a condenser; an evaporator; a flowpath from the condenser to the evaporator; and a liquid-to-suction heat exchanger in the flowpath.
 2. The air-conditioner according to claim 1, wherein the air-conditioner is a portable air-conditioner.
 3. The air-conditioner according to claim 1, further comprising a four-way valve configured to reverse a flow of the air-conditioner to allow the air-conditioner to provide both heating and cooling.
 4. The air-conditioner according to claim 1, wherein a liquid line to the liquid-to suction heat exchanger is arranged inside of a saturated vapour line that comes from the evaporator.
 5. The air-conditioner according to claim 4, wherein a liquid line comprises fins on the outside of the liquid line. 